1. Field of the Invention
The invention relates to a method for making rotors for screw-type machines, in particular rotors having a large flight depth and a small pitch.
2. Description of the Related Art
In the area of machinery, screw-type machines are increasingly replacing the reciprocating-piston or gear machines hitherto used in many areas. The known piston compressor, for example, has been replaced by screw-type compressors in the industry. Similarly, screw pumps have replaced gear-type lubricating oil pumps in industrial plants.
All screw-type machines have a rotor which, in conjunction with one or more secondary rotors and/or the surrounding casing, forms closed delivery chambers into which a medium being conveyed is transported from an inlet side to an outlet side of the machine. Rotors of this type have hitherto been produced on milling or grinding machines by the hobbing method. This production method has been technically and commercially useful for rotors of screw compressors or for screw pumps for lubricating oil which have a large pitch in combination with a small flight depth and are produced in large quantities. In this case, a corresponding machining tool (profile milling cutter or formed wheel) is required for each rotor geometry (diameter, pitch, profile shape). The resulting tool costs and set-up times are acceptable for large scale production.
However, when producing rotors with a large flight depth and a small pitch which are produced individually or in very small quantities for special machines, the above-mentioned method is particularly costly, because of the tool costs and set-up times. In the case of special flank profiles, as described for a feed screw pair, e.g. in DE 42 24 969 C1, technical feasibility is limited to a considerable extent when using the above production method.